This invention relates to controlled oscillators and more particularly relates to such oscillators in which oscillator gain is controlled.
In communication systems today, a wide range of frequencies is employed in controlled oscillators, such as voltage controlled oscillators (VCOs). Typically, such VCOs are employed in phase locked loops. The VCOs generate frequencies over a wide range in response to a control voltage, Vc. The ratio of a change in the oscillator frequency to a change in Vc is known as the VCO gain or Kvco.
The range of Vc is limited by the supply voltage, which typically is small in the integrated circuits used in communication systems. In known systems, Vc is substantially smaller than the supply voltage. In the known systems, if a large frequency range must be generated in response to a small Vc range, then Kvco must have a relatively large value. However, a large Kvco value results in the other problems. For example, as the Kvco value increases, oscillator instability and phase noise also increase. In known systems, Kvco also tends to be non-linear. This problem increases the complexity of the circuitry required to accurately control the output frequency.
The inventor has discovered a technique for solving these problems and for keeping Kvco at a relatively small and relatively constant value, thereby increasing the accuracy of the output frequency and reducing the complexity of related circuitry.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.
One apparatus embodiment of the invention is useful to generate a variable frequency output signal in response to a control signal. For such an application, the embodiment comprises an oscillator arranged to generate the output signal with a frequency adjustable within a first frequency range in response to a first parameter value of an operating parameter and adjustable within a second frequency range in response to a second parameter value of the operating parameter. The frequency is generated within the first frequency range and the second frequency range in response to a control value of the control signal. The control value is within a predetermined control value range. A first circuit is arranged to adjust the parameter values of the operating parameter. A second circuit is arranged to control a ratio of the frequency to the control value within at least the first frequency range.
One method embodiment of the invention is useful for generating a variable frequency output signal in response to a control signal. For such an application, the embodiment comprises generating the output signal with a frequency adjustable within a first frequency range in response to a first parameter value of an operating parameter and adjustable within a second frequency range in response to a second parameter value of the operating parameter. The frequency is generated within the first frequency range and the second frequency range in response to a control value of the control signal. The control value being within a predetermined control value range. The parameter values of the operating parameter are adjusted. A ratio of the frequency to the control value is controlled within at least the first frequency range.
By using the foregoing techniques, controlled oscillators can be made with a degree of accuracy previously attainable only by much more complex and costly devices.
These and other advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings.